In general, there are conduction, convection and radiation as a heat transfer mechanism. Conduction heat is mainly transferred by solid and convection heat is mainly transferred by fluid. In addition, radiation heat is transferred through a process of discharging energy formed of electromagnetic waves emitted from surface of a certain heating unit, in which heat is emitted at velocity of light even at a state of having no medium and is delivered directly to an object. Wavelength of the radiation heat ranges from an infrared ray region to an ultraviolet ray region whose wavelength is the shortest via a visible ray region. However, in comparison with the visible or ultraviolet ray, it has been known that a band of the wavelengths of the infrared rays such as far infrared rays, middle infrared rays, and near infrared rays has the strongest heating function.
Therefore, conventional cooking appliances using infrared rays have been developed in various forms.
One example of an existing infrared ray cooking appliance was disclosed in Korean Patent Registration No. 10-779225 published on Nov. 28, 2007. The infrared ray meat grill cooker disclosed in the Korean Patent Registration No. 10-779225 includes: an infrared lamp whose outer portion is composed of a quartz tube; a cooking pan that is placed over the infrared lamp; and a reflective board that is placed below the infrared lamp. The infrared ray meat grill cooker employs a uni-direction heating method in which the infrared lamp heats the cooking pan and the cooking pan grills only a lower portion of meat. As a result, the infrared ray meat grill cooker may cause inconveniences that meat must be turned over constantly in order to prevent the meat from being burnt excessively. In addition, a thermal efficiency may fall.
Another example of a cooking appliance developed using infrared ray technology was Korean Utility-model Registration No. 20-314608 published on May 27, 2003. The meat roaster disclosed in the Korean Utility-model Registration No. 314608 has a near-infrared ray lamp that is positioned at a certain distance over a gridiron grilling pan and a reflective board over the infrared ray lamp. The meat roaster applies near-infrared rays directly onto meat from the above infrared ray lamp and successfully keeps meats from burning. Accordingly, the meat roaster has an advantage that even the inner portion of the meat can be roasted evenly. However, the meat roaster also employs a uni-direction heating method in which the near-infrared rays emitted from the near-infrared ray lamp roasts only an upper portion of meat, to thereby cause inconveniences that meat must be turned over constantly in order to prevent the meat from being burnt excessively.
Moreover, in the case of these cooking pans using the infrared rays or near-infrared rays, there is a problem of delaying time taken to roast foods put on the cooking pans. In addition, since the infrared ray lamps or near-infrared ray lamps should be turned on for a long time in order to heat foods put on the cooking pans, there is also a problem that an expense burden is additionally caused by an increase of electric charges.
Meanwhile, still another example of an existing infrared ray cooking appliance was disclosed in Korean Patent Application No. 10-2009-0006812 filed by the same applicant as that of this application. The bidirectional heating cooker disclosed in the Korean Patent Application No. 10-2009-0006812 includes: a base frame that forms a lower framework; a supporting pillar that is vertically placed at the center of the upper surface of the base frame; a cooking pan that is separably placed on an upper portion of the base frame, and at the center of which a center hole through which the supporting pillar passes is formed; a cover that is provided at the upper end of the supporting pillar; an upper heating unit that is placed on the lower portion of the cover and emits radiant heat toward the cooking pan; and a lower heating unit that is provided at the lower end of the cooking pan and transfers heat directly to the cooking pan, in which the cooking pan is heated by radiant heat irradiated from the upper heating unit and is directly heated by the lower heating unit, and both lower and upper portions of food are simultaneously roasted by radiant heat irradiated from the upper heating unit and by direct heating of the lower heating unit.
Thus, the bidirectional heating cooker disclosed in the Korean Patent Application No. 10-2009-0006812 can roasts the upper and inner portions of food by the upper radiation unit and the lower heating unit, and has advantages that a thermal efficiency is excellent, foods such as meat for roasting can be evenly roasted without excessive burning although they are not continuously turned over, and thus little amount of smoke or odor is produced during cooking, in comparison with the conventional uni-directional infrared ray cooker.
However, the bidirectional heating cooker disclosed in the Korean Patent Application No. 10-2009-0006812 has a disadvantage that the cooking pan can be put on the lower heating unit only in the case the upper radiation unit is separated from the supporting pillar that is connected with the lower heating unit. That is, the cooking pan that has been put on the upper portion of the lower heating unit can be separated from the lower heating unit or the cooking pan can be replaced by another cooking pan, in order to make the cooking pan washed or replaced, only when the upper radiation unit is separated from the supporting pillar, thereby lowering conveniences of use.
In other words, since a coupling structure of the cooking pan is formed into a structure of inserting and fitting the upper portion of the supporting pillar through the center hole formed at the inner-center of the cooking pan, in the case of the bidirectional heating cooker disclosed in the Korean Patent Application No. 10-2009-0006812, the upper radiation unit should be necessarily separated from the supporting pillar when the cooking pan is separated from or coupled with the lower heating unit, to accordingly cause lowering of conveniences of use.
Further, although the bidirectional heating cooker disclosed in the Korean Patent Application No. 10-2009-0006812 has a structure of putting the cooking pan on the lower heating unit, it has a drawback that various types of cooking pans cannot be used in order to simultaneously cook different kinds of foods such as a roast food, a pot stew food, or a casserole food, due to reasons that each type of a cooking pan cannot be easily replaced with another one, and that the various types of cooking pans cannot be used in combination.